Wednesday, August 13, 2008

The mechanics of shared parking

This will hopefully be my last post about 315 W. Ponce. I'm going to try and explain how shared parking works, since not everyone who reads this is a real estate junkie. I'm going to be referring to the parking study for the 315 W. Ponce development(pdf) if you want to follow along.

Basically, the premise is that you never need all the parking required for a mixed-use development because different users need parking at different times. At night, residential and retail users need spaces. During the day, retail and office users need spaces. So the residential and the office users can share spaces. Obviously, some number of apartment folks will not be gone during the day, or will leave their car at home for whatever reason. So you can't share all the spaces. But you can share some of them.

Obviously, the success of shared parking depends a lot on the math for individual projects. Let's look at 315 W. Ponce, since I've been talking about it. First, let's assume that everybody who ever needed to park at 315 W. Ponce needed to park there at the same time:

Maximum use

Office 240
Residential 330
Retail 35



Like I said, you won't ever need all of these spots. During the day, you need enough space for all your office folks, plus all your retail shoppers. How many spaces should you keep for the folks who leave/need their car at home during the day? The parking study assumes that 40% of apartment folks will keep their cars at home. Let's see how that looks:

Day-time Peak Use

100% office users 240
40% residential users 132
100% retail users 35



This is how they end up justifying a 428 space parking deck. They've even included at 21 space cushion, in addition to the 22 surface lot spaces that will be left after redevelopment. I think 40% is quite a reasonable assumption, but if there is a weak point here, that would be it. Still, I would not want to be the one arguing that half of the residents would need to leave their car at home all day. It wouldn't look like any apartment complex I've ever seen.

What about at night time? This is beyond the scope of the 315 W. Ponce parking study, but let's go through the same procedure. Let's assume that 20% of the office workers stay late and need to park their cars in the deck in the evening. Then, let's factor in all the residential users and all the retail shoppers:

Night-time Peak Use

20% office users 48
100% residential users 330
100% retail users 35



We are still under the 428 spaces in the deck. This is why 315 W. Ponce won't create excess parking issues for the neighborhood.

For statistical junkies, the parking study uses existing traffic counts for the office building and a 1.5 space/unit, which is actually greater than the 60% one-bedroom unit mix might need. For a 1 space/bedroom ratio, they would only need a 1.4 space/unit ratio, or 308 spots. The extra spaces accommodate guests, but if a developer were trying to "cook the books" on parking numbers they could do so here. The fact that they don't suggests they are on the up and up. The study also uses a 5 spaces/1,000 sf of retail, which is typical of retail projects. Some urban projects try and get away with less, counting on people walking, etc. The ratios here is also very dependent on what type of tenants.

The more I look at these numbers, the more I think the opposition is about any development on this site, period. The argument about excess parking doesn't hold water, in my book, although I guess that is up for debate. I think the parking study is very reasonable, and I find the objections overwrought.

Decatur Metro has a good post explaining why this site in particular is special. I for one would appreciate a discussion on the merits of infill development in historic areas, instead of arguing over the finer points of New Urbanism. As it is, the opponents come off as obstructionists and bullheaded, which is a shame. I am sure there are good points to be made about the historic nature of the area that are unrelated to the parking issue, but they get overshadowed because the neighborhood has chosen to make their stand on parking.

Of course, feel free to ignore me. Apparently because I own a car I can't talk about this stuff.


  1. As an FYI, there is at least one little-known case of shared parking working in Atlanta. The Post Biltmore apartment building in Midtown leases out access to its deck to daytime tenants of the Biltmore Hotel (now offices) -- who of course are there when most of the residents are away. This is only possible because parking spaces are not assigned to individual residential tenants on an exclusive basis (as is typically the case w/ condos, though that needs to change).

    I actually lived at Post Biltmore for a while and the arrangement seemed to work out quite well. The parking deck was consistently at about 80% to 90% capacity around the clock, which is basically the ideal condition for any urban parking facility.

    This was two or three years ago but as far as I know the arrangement is still in place. It's certainly preferable to the Biltmore offices doing a giant deck of its own.

  2. I say this as someone who's merely watching the events unfold and looking for discussion, not as a part of my reporting duties. Just had to throw that disclosure out there.

    I recall a lot of residents also being concerned about what would happen when or if the development made the switch from apartments to condos. With an apartment, you are usually guaranteed a space. But when you buy a condo, a space is included as part of the purchase. It's yours.

    Before it decided to table JLB Partners' parking variance request, the city's zoning board of appeals told the developer that it'd have to come before them again if it made the switch from apartments to condo for just such a reason. The developer's representative said he'd be willing to accept that requirement. I wondered how that would play into things.


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